The when has been known for many many years if anyone bothers to look up financial year Thailand for individual taxpayers.... its always been Jan 1 to Dec 31.
The who will be (I assume) enforcement of tax laws also been in place for many years, this announcement is merely closing the loop holes used to avoid them.
The how will be same as any other country.... lodge a tax return by the due date, in this instance it will be 31/03/25.
Or something like that anyways !